Re: [ATM] More on aperature stops

["Arjan te Marvelde" <arjan.te.marvelde@hetnet.nl>]

Mel,

> > http://www.designwizardry.com/aperaturedifference.jpg
> > I'm pretty sure that the image on left is pretty much
> > what most people see with a 10" f/4.7 newtonian at
> > 7.5mm with questionable atmospheric conditions with no
>
> That's really a horrible image.  Any decent 10 inch will give a far
superior
> image.  That smear to the immediate lower lower-right of Mars indicates
> horrible thermal problems adjoining the optics.  The larger smear is
> indicative of scattering, poor baffling, and a bad eyepiece that's
ghosting
> on you (could be a poorly cleaned eyepiece).
>
> You'll do better to tackle the problems of this 10 inch head-on, learning
> from them, than trying to run and hide from them by using an off-axis
mask.
>

I saw the same effect (though not as bad) looking at Mars, and concluded
that my scope needs some more anti-scatter measures. I would have expected
the same effect to happen when watching the moon, but the terminator and
edge appear razorsharp, using exactly the same setup.
This puzzles me, what else than scatter could cause the halo? I would expect
the scatter to be proportional to the amount of light, so no non-linearity
issue. Maybe it is the decreased eyepupil due to the greater intensity of
the moonlight?

/Arjan

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